Shadow Mission "Secondary"

Does "Secondary" refer to Intermediate? If not, then what?

im sure it means that both normal reward and building stone comes out together, sort of like personal enchant scroll.

For example, forest golem crystal and building stone.

i think.

Yeah, that makes sense. I was running Stones of Sliab Cuilin with a friend, and every single run resulted in a Building Stone with a regular reward of that mission in our chests. Thanks. :D

The golems in Other Alchemist Basic spam drop them. No other difficulty of Other Alchemist drops it sadly...

so, i assume the secondary rewards is like the second alchemy scrap in that part of g9

Pretty much. From my experiences lately, it's guaranteed you'll receive one from the reward chest of whatever mission it comes from alongside the usual reward (i.e. Thunder Crystal).